This invention relates to apparatus for printing patterns on cans and similar cylindrical objects and more particularly to a can printer having a linear conveyor with the printing stations spaced longitudinally along the linear conveyor.
Recently, rotary can printers have been extensively used for printing patterns on cans. A typical rotary printer has a plurality of mandrels on a mandrel drum. The mandrels carry the cans into contact with a rotating printing blanket. Examples of such rotary can printers are shown in U.S. Pat. Nos. 3,587,816 - Russell et al and 3,496,863 - Cvacho et al.
It is often desirable to print a multiple colored pattern on a can. In this case, the different colors are printed at different printing stations. Usually, it is desirable that each color be at least partially dried before the next color is printed in the pattern. Rotary can printers are not suitable for this because there is not sufficient room between printing positions to allow drying, or if large distance is allowed, then the drum would be of an inconveniently large diameter.
Another problem with rotary can printers is that the printing stations are crowded around the periphery of the drum and access to them is difficult. It is quite difficult to remove one printing station without completely disrupting the operation of the printer.
Linear conveyors are extensively used in can handling. U.S. Pat. No. 2,718,847 - Jackson et al shows a linear conveyor carrying bottles past a printer. However, the printer is of the rotary type in which the patterns to be printed are impressed upon a rotating printing blanket which contacts the bottles. This type of printer suffers from the same disadvantages discussed above with respect to rotary printers.
One reason for the apparent lack of use of linear conveyor printers in the prior art is the problem of obtaining good registration between the can pattern and printing blanket. Prior art linear conveyors have not provided the precise timing and registration necessary for a multiple printing operation.
Another reason that linear conveyors have not been used in can printers is that a conveyor chain normally produces a jerky motion. The standard type of drive chain used in conveyors must, of necessity, be allowed a certain amount of slack for proper functioning and wear. Slack between the chain link and the sprocket is inherent in normal conveyors and it causes the chain to move at changing speeds. Because of this, such prior art conveyors do not have the accuracy required to maintain precise registration of a printing mandrel with a printer.